Mattress



FIG. 1 is a perspective view of a mattress;

FIG. 2 is a back end view of the mattress, the front end view being identical thereto;

FIG. 3 is a left side view of the mattress, the right side view being identical thereto; and,

FIG. 4 is a bottom view of the mattress.

The broken lines shown in the drawings are included for illustrating portions of the mattress and forms no part of the claimed design. 

CLAIM The ornamental design for a mattress, as shown and described. 